Oil recovery process utilizing superheated steam

ABSTRACT

A secondary recovery process in which steam or superheated steam generated from a mixture of fresh, brackish or brine water and a heavy hydrocarbon or mixture of heavy hydrocarbon compounds is injected into an oil-bearing formation and oil is recovered from a producing well located at a substantial distance from the injection well.

I Umted States Patent 1191 1111 3,768,558 Allen et al. Oct. 30, 1973 [54] OIL RECOVERY PROCESS UTILIZING 3,259,186 7/1966 Dietz 166/272 X SUPERHEATED S M 3,350,299 /1967 Hess et a]. 2l0/22 3,350,300 10/1967 Hess et al. 1. 210/22 Inventors: J p Allen, Bellalre; Thomas 3,685,581 8/1972 11655 et al. 166/272 Teasdle bmh FOREIGN PATENTS OR APPLICATIONS Assigneei Texaco -1 New York, 511,768 8/1939 Great Britain 166 263 [22] Filed: June 30, 1972 Primary Examiner-Stephen J. Novosad H PP 2671798 Art0meyThomas I-I. Whaley et al.

52 us. 01. 166/272, 166/303 [571 ABSTRACT [51] Int. Cl. E2lb 43/24 A secondary recovery process in which steam or su- [58] Field of Search 166/263, 272, 303; perheated steam generated from a mixture of fresh, 210/22 brackish or brine water and a heavy hydrocarbon or mixture of heavy hydrocarbon compounds is injected [56] References Cited into an oil-bearing formation and oil is recovered from UNITED STATES PATENTS a producing well located at a substantial distance from 2,862,558 12/1958 Dixon 166/272 the 3,193,009 7/1965 Wallace et al. 166/272 7 Claims, 1 Drawing Figure '2 HEATER 4 M HYDRO- m 21 11 12 w wt; 34 I8 14 A HE -rrrrr4 3 am: m

2 5:." K 6) 4e I6- i i l 50) OIL RECOVERY PROCESS UTILIZING 'SUPERI-IEATED STEAM BACKGROUND OF THE INVENTION This invention relates to an oil recovery process and, in particular, it relates to a secondary oil recovery process in which steam or superheated steam is employed as the driving fluid.

PRIOR ART Various secondary methods have been proposed for stimulating the flow of oil as well as inducing driving forces effective to increase the recovery of oil from producing wells.

In its simplest form this involves the introduction into an injection well of suitable flooding material under sufficient pressure to impose a substantial driving force against the reservoir oil. This, for example, has been carried out with gaseous and liquid materials, notably with natural gas or with water.

More recently, however, improved results have been obtained by injecting steam into the producing formation. Also, it has been proposed to introduce hydrocarbons which are lighter than and have a lower viscosity than the reservoir hydrocarbons. In fact, it has been found that usually a small, thin layer of hydrocarbon liquid ahead of the more prosaic driving flood such as water, natural gas or steam, has tended to improve ultimate production from a spaced producing well.

Also among variations that have been proposed is the introduction of a mixture of steam and hydrocarbon vapors under low pressure. This process, as well as prior related processes heretofore disclosed, are described in US. Pat. No. 2,862,558 in which a mixture of steam and kerosene was injected into a tar sand formation at a temperature of about 225500F and at a pressure of at least. 20 psig.

One particular problem which arises in steam flood-- ing is that a substantial source of fresh water with a low solids content must be available. This poses a particular problem in areas where only small quantities of fresh water are available and where brine is produced in oil recovery operations. Such saline waters are so high in solids content and are so corrosive to oil field equipment that their use in steam generation is not generally feasible.

It would be more efficient to employ superheated steam rather than steam saturated with water in petroleum recovery. However, a number of problems arise in connection with the use of superheated steam. Generation of superheates steam from saturated steam for injection purposes requires very elaborate and expensive auxiliary equipment. All liquid water must be separated from the saturated steam which necessitates multi-stage separation and to assure complete water removal the temperature is sometimes lowered to precipitate additional water in order to improve the extraction of the associated mist. All of these operations reduce the thermal efficiency of the process. Carryover of water containing dissolved solids will result in failure of the superheater due to solids deposition. The superheater requires very expensive metal guards and construction techniques for further assurance of continuous and effective superheating of the incoming 100 percent saturated steam.

Conventional steam boilers usually require a continuous watch with intermittent blow down .of the water containing concentrated dissolved solids. In typical steam flooding operations continuous throughput steam generators are used which produce about percent quality steam and the entire efflux, including 20 percent water containing concentrated dissolved solids, is injected into the oil-bearing formation. In many instances the concentration of dissolved solids is high causing accumulation of solids, plugging of injection lines and/or the oil-bearing formation. Large and expensive steam-water separation equipment is required if it is desirable to inject saturated steam alone at the high temperatures and pressures that are required. Maintenance of the necessary controls in good operation condition is also difficult.

BRIEF STATEMENT OF THE INVENTION The recovery process of this invention in which oil is recovered from a subterranean oil-bearing formation comprises:

a. forming from a mixture of heavy hydrocarbons and feed water containing dissolved solids under the influence of elevated temperature and pressure a waterhydrocarbon phase substantially free of the feed water dissolved solids and a separate water phase,

b. separating the said water phase containing the dissolved solids from the said hydrocarbon-water phase,

c. reducing the pressure on the said waterhydrocarbon phase and then heating the resulting mixture, thus forming a saturated or superheated steam phase and a hydrocarbon liquid phase,

d. separating the said steam phase from the hydrocarbon liquid phase,

e. injecting the said steam directly into the said oilbearing formation, and

f. producing oil from the said formation.

The process of this invention is not only applicable as a well stimulation process but also may be utilized in oil recovery operations where the steam is injected into an oil-bearing formation via an injection well, and oil is recovered via a production well located a substantial distance from the said injection well.

In the process of this invention water high in solids content, such as field brine, can be employed as feed water to prepare the initial water-hydrocarbon phase since in the preparation of this phase substantially all of the initially present solids in the feed water portion thereof are partitioned from the water-hydrocarbon phase into the separate water phase not utilized in the preparation of the steam. Thus, any problems of formation pore plugging because of solids carryover in the steam or plugging problems in apparatus lines are avoided.

Generating superheated steam in accordance with step ('c) above eliminates the problems encountered with superheated saturated steam alone. The water in the water-hydrocarbon phase is substantially free of feed water dissolved solids which removes the possibility of solids deposition in the superheater. Since a hydrocarbon liquid phase is always present, this eliminates dry heating across metal guards during the superheating operation which, in turn, permits the use of less elaborately designed and less expensive superheaters. Likewise, multistage separation of saturated steam and water is eliminated, thereby further reducing costs.

Injection of superheated steam as practiced in this invention results in the injection of more heat per unit weight than with a mixture of steam and water and, in

addition, a higher thermal efficiency is achieved. The higher temperatures developed in the formation cause the connate water which is usually the wetting phase to flash to steam. This violent mechanical action moves oil into the major flow channels where it can be more efficiently displaced to producing well bores.

A wide variety of hydrocarbons are suitable for use in the process of this invention. The useful heavy hydrocarbons have high molecular weights and possess low vapor pressures or fugacities. Heavy hydrocarbons having from about 16 to about 40 carbon atoms and having boiling points between about 400F and about 650F are preferred. Examples of individual hydrocarbon types which can be used in the process of the present invention, either alone or in admixture with one another are paraffin waxes, naphthalene, octadecane, eicosane, docosane, tetracosane, octacosane, nonacosane, etc.

The water-hydrocarbon liquid phase solution utilized to prepare the superheated steam or'the homogenous water-hydrocarbon phase as it has been referred to above is an intimate intermixture. As previously pointed out, the superheated steam employed in this invention is prepared from the so-called homogenous water-hydrocarbon phase previously described. This homogeneous liquid water-hydrocarbon phase has been referred to as an intimate intermixture or intersolution of two normally repugnant liquids. The preparation of such intersolutions has been described in detail in the following US. Pat:

No. 3,316,172; No. 3,318,805; No. 3,325,400; No. 3,350,299 and No. 3,350,300.

The preparation of the liquid water-hydrocarbon phase involves the extraction of water from the field water, such as brine containing a high concentration of dissolved solids, by a hot hydrocarbon liquid at a high temperature at which such hydrocarbon liquids are capable of selectively absorbing or dissolving a substantial proportion of water. Another requirement, of course, is that the elevated temperatures required must be accompanied by pressures sufficient to maintain both the heavy hydrocarbon and water in liquid phase condition. The temperatures involved are considerable, normally in the region substantially above 500F and with the pressures accordingly above 1,000 psig.

With respect to the combined liquid waterhydrocarbon phase employed in this invention for the preparation of the saturated steam or superheated steam, applicants do not desire to be bound by any statement regarding its precise molecular nature, whether solution or whatever other form it may be. It can, however, be asserted that this combination is in fact a liquid phase under the conditions noted and therefore as has been hitherto explained, it may be referred to simply as a phase in which the hydrocarbon forms a complex with water.

Inasmuch as the complexing operation has been thoroughly described and explained in the aforementioned patents, no further details are supplied herein other than to make reference to such above-listed patents for full description of such details and, by reference, to make such disclosure.

The FIGURE illustrates one arrangement of apparatus for carrying out the process of this invention.

A heavy hydrocarbon in liquid phase, such as eicosane heated to a temperature of about 145F, is introduced via line 2 into pump 4 which brings the pressure of the system up sufficiently to maintain the system in liquid phase condition at the temperatures involved. Similarly, field water or brine containing a high percentage of solid materials is introduced into pump 8 via line 6 where the pressure is brought up to the system pressure. The liquid hydrocarbon oil discharged from pump 4 is then passed through circulating pump 10 and heater 12 where it is raised above the critical high temperature in the range aforementioned at which the hydrocarbon oil assumes a high extractive affinity for water. The hot oil is then transferred from heater 12 through pipe 14 into the lower portion of column 16, a portion of which, as hereinafter indicated, passing continuously upward through column 16 and out through line 18, from whence it is re-introduced into line 2.

The feed water or brine stream is discharged from pump 8 via line 8a into heat exchanger 32 from which it is discharged via line 8b into spray head 20 situated in the upper end of column 16 downwardly through the upflowing column of hydrocarbon oil.

As a result of this interaction of the two streams, therefore, the upflowing hot hydrocarbon oil continuously heats the downflowing brine so that at an intermediate level in the column the two streams have reached a complexing temperature (i.e., the temperature at which clear water-hydrocarbon of, for example, 575F at 2,000 psi.) This, in the present design, may take place at the position in the spray column just below downcomer 24, from which outlet line 26 extends.

Therefore, flowing through the line 26 is a high pressure, high temperature complex of hydrocarbon and water, namely a continuous, clear phase comprising a solution, extract, or whatever the case may be, or molecularly intermingled oil and water. The waterhydrocarbon phase, as previously pointed out, inherently rejects the soluble content of the feed water and the insoluble salts precipitated settle donwwardly into sludge chamber 28 at the bottom of column 16. The solid material forms a relatively concentrated solution in excess brine fed to the system, or, depending upon the amount of the excess feed water, a gelatinous floc.

The insoluble materials as a part of a concentrated brine mixture are continuously removed from the system via line 30 and passed through heat exchanger 32 where the hot concentrated brine mixture heats the incoming field water. From heat exchanger 32 the brine mixture is passed to blowdown valve 32d via line 32c and finally the brine mixture is removed from the system via line 34 and sent to an appropriate waste disposal system not shown. Generally, about 60 to about percent of the total volume of the hydrocarbon and water separate out as the concentrated solution or phase containing the precipitated solids.

The homogeneous water-hydrocarbon phase withdrawn from column 16 via line 26 is passed through letdown valve 44 where the pressure is reduced to about 700 psig causing the water present to flash to steam. The resulting steam-liquid hydrocarbon mixture is then passed into heater 46 by means of line 45 where sufficient heat is added to form a mixture consisting'of superheated steam and liquid hydrocarbon at a temperature of about 600F and 700 psig. From heater 46 the mixture is sent to separator 48 via line 47. Superheated steam which is removed overhead from separator 48 by line 52 is introduced into well pipe 36 controlled by suitable valves not shown. By means of well pipe 36 the superheated steam is introduced directly into the producing formation 38 at the bottom of the well where it proceeds to intermingle with the hydrocarbons of the reservoir and drive them a second or producing well 40, causing the produced constituents to flow upwardly in the well and be recovered through line 42. The bottoms product from separator 48 which is a liquid heavy hydrocarbon stream is introduced by means of line 50 into pump 51 where the pressure is raised to system pressure in line 2 and the liquid heavy hydrocarbon stream is passed from pump 51 via line 54 into line 2.

What is claimed is:

1. A process for the recovery of oil from a subterranean oil-bearing formation which comprises:

a. forming from a mixture of heavy hydrocarbons and feed water containing dissolved solids under the influence of elevated temperature and pressure a water-hydrocarbon phase and a separate water phase.

b. separating the said water phase containing the dissolved solids from the said hydrocarbon-water phase,

c. reducing the pressure on the said waterhydrocarbon phase and then heating the resulting mixture thus forming a steam phase and a hydrocarbon liquid phase,

d. separating the said steam phase from the hydrocarbon liquid phase,

e. injecting the said steam directly into the said oilbearing formation, and

f. producing oil from the said formation.

2. The method as defined in claim 1 wherein in step (c) sufficient heat is added to the resulting mixture to form superheated steam and a hydrocarbon liquid phase.

3. The method as defined in claim 1 wherein said oil is recovered from a producing well located a substantial distance from said injection well.

4. The method according to claim 1 wherein said oil is produced from said formation by terminating said injection step and withdrawing oil from said reservoir via the injection well.

5. The method according to claim 1 wherein said heavy hydrocarbon water phase is prepared by heating a mixture of the light hydrocarbon and to a temperature of at least 500F and under a pressure of about 2000 to 2700 psig.

6. The method according to claim 1 wherein the said mixture of heavy hydrocarbon and feed water is brought to the elevated temperature condition in step (a) by continuously heating the light hydrocarbon stream and by bringing the feed water stream into direct contact with the hot heavy hydrocarbon, such that the boiler scaling is obviated.

7. The method according to claim 1 wherein the hydrocarbon employed is eicosane. 

2. The method as defined in claim 1 wherein iN step (c) sufficient heat is added to the resulting mixture to form superheated steam and a hydrocarbon liquid phase.
 3. The method as defined in claim 1 wherein said oil is recovered from a producing well located a substantial distance from said injection well.
 4. The method according to claim 1 wherein said oil is produced from said formation by terminating said injection step and withdrawing oil from said reservoir via the injection well.
 5. The method according to claim 1 wherein said heavy hydrocarbon water phase is prepared by heating a mixture of the light hydrocarbon and to a temperature of at least 500*F and under a pressure of about 2000 to 2700 psig.
 6. The method according to claim 1 wherein the said mixture of heavy hydrocarbon and feed water is brought to the elevated temperature condition in step (a) by continuously heating the light hydrocarbon stream and by bringing the feed water stream into direct contact with the hot heavy hydrocarbon, such that the boiler scaling is obviated.
 7. The method according to claim 1 wherein the hydrocarbon employed is eicosane. 